// The github repo where I got this was licensed under the MIT license, of which the license text is shown below.
// https://github.com/veorq/SipHash/tree/master
// Copyright 2012-2024 JP Aumasson

// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


/*
   SipHash reference C implementation

   Copyright (c) 2012-2022 Jean-Philippe Aumasson
   <jeanphilippe.aumasson@gmail.com>
   Copyright (c) 2012-2014 Daniel J. Bernstein <djb@cr.yp.to>

   To the extent possible under law, the author(s) have dedicated all copyright
   and related and neighboring rights to this software to the public domain
   worldwide. This software is distributed without any warranty.

   You should have received a copy of the CC0 Public Domain Dedication along
   with
   this software. If not, see
   <http://creativecommons.org/publicdomain/zero/1.0/>.
 */

#include "siphash.h"
#include <assert.h>
#include <stddef.h>
#include <stdint.h>

/* default: SipHash-2-4 */
#ifndef cROUNDS
#define cROUNDS 2
#endif
#ifndef dROUNDS
#define dROUNDS 4
#endif

#define ROTL(x, b) (uint64_t)(((x) << (b)) | ((x) >> (64 - (b))))

#define U32TO8_LE(p, v)                                                        \
    (p)[0] = (uint8_t)((v));                                                   \
    (p)[1] = (uint8_t)((v) >> 8);                                              \
    (p)[2] = (uint8_t)((v) >> 16);                                             \
    (p)[3] = (uint8_t)((v) >> 24);

#define U64TO8_LE(p, v)                                                        \
    U32TO8_LE((p), (uint32_t)((v)));                                           \
    U32TO8_LE((p) + 4, (uint32_t)((v) >> 32));

#define U8TO64_LE(p)                                                           \
    (((uint64_t)((p)[0])) | ((uint64_t)((p)[1]) << 8) |                        \
     ((uint64_t)((p)[2]) << 16) | ((uint64_t)((p)[3]) << 24) |                 \
     ((uint64_t)((p)[4]) << 32) | ((uint64_t)((p)[5]) << 40) |                 \
     ((uint64_t)((p)[6]) << 48) | ((uint64_t)((p)[7]) << 56))

#define SIPROUND                                                               \
    do {                                                                       \
        v0 += v1;                                                              \
        v1 = ROTL(v1, 13);                                                     \
        v1 ^= v0;                                                              \
        v0 = ROTL(v0, 32);                                                     \
        v2 += v3;                                                              \
        v3 = ROTL(v3, 16);                                                     \
        v3 ^= v2;                                                              \
        v0 += v3;                                                              \
        v3 = ROTL(v3, 21);                                                     \
        v3 ^= v0;                                                              \
        v2 += v1;                                                              \
        v1 = ROTL(v1, 17);                                                     \
        v1 ^= v2;                                                              \
        v2 = ROTL(v2, 32);                                                     \
    } while (0)

#ifdef DEBUG_SIPHASH
#include <stdio.h>

#define TRACE                                                                  \
    do {                                                                       \
        printf("(%3zu) v0 %016" PRIx64 "\n", inlen, v0);                       \
        printf("(%3zu) v1 %016" PRIx64 "\n", inlen, v1);                       \
        printf("(%3zu) v2 %016" PRIx64 "\n", inlen, v2);                       \
        printf("(%3zu) v3 %016" PRIx64 "\n", inlen, v3);                       \
    } while (0)
#else
#define TRACE
#endif

/*
    Computes a SipHash value
    *in: pointer to input data (read-only)
    inlen: input data length in bytes (any size_t value)
    *k: pointer to the key data (read-only), must be 16 bytes 
    *out: pointer to output data (write-only), outlen bytes must be allocated
    outlen: length of the output in bytes, must be 8 or 16
*/
int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
            const size_t outlen) {

    const unsigned char *ni = (const unsigned char *)in;
    const unsigned char *kk = (const unsigned char *)k;

    assert((outlen == 8) || (outlen == 16));
    uint64_t v0 = UINT64_C(0x736f6d6570736575);
    uint64_t v1 = UINT64_C(0x646f72616e646f6d);
    uint64_t v2 = UINT64_C(0x6c7967656e657261);
    uint64_t v3 = UINT64_C(0x7465646279746573);
    uint64_t k0 = U8TO64_LE(kk);
    uint64_t k1 = U8TO64_LE(kk + 8);
    uint64_t m;
    int i;
    const unsigned char *end = ni + inlen - (inlen % sizeof(uint64_t));
    const int left = inlen & 7;
    uint64_t b = ((uint64_t)inlen) << 56;
    v3 ^= k1;
    v2 ^= k0;
    v1 ^= k1;
    v0 ^= k0;

    if (outlen == 16)
        v1 ^= 0xee;

    for (; ni != end; ni += 8) {
        m = U8TO64_LE(ni);
        v3 ^= m;

        TRACE;
        for (i = 0; i < cROUNDS; ++i)
            SIPROUND;

        v0 ^= m;
    }

    switch (left) {
    case 7:
        b |= ((uint64_t)ni[6]) << 48;
        /* FALLTHRU */
    case 6:
        b |= ((uint64_t)ni[5]) << 40;
        /* FALLTHRU */
    case 5:
        b |= ((uint64_t)ni[4]) << 32;
        /* FALLTHRU */
    case 4:
        b |= ((uint64_t)ni[3]) << 24;
        /* FALLTHRU */
    case 3:
        b |= ((uint64_t)ni[2]) << 16;
        /* FALLTHRU */
    case 2:
        b |= ((uint64_t)ni[1]) << 8;
        /* FALLTHRU */
    case 1:
        b |= ((uint64_t)ni[0]);
        break;
    case 0:
        break;
    }

    v3 ^= b;

    TRACE;
    for (i = 0; i < cROUNDS; ++i)
        SIPROUND;

    v0 ^= b;

    if (outlen == 16)
        v2 ^= 0xee;
    else
        v2 ^= 0xff;

    TRACE;
    for (i = 0; i < dROUNDS; ++i)
        SIPROUND;

    b = v0 ^ v1 ^ v2 ^ v3;
    U64TO8_LE(out, b);

    if (outlen == 8)
        return 0;

    v1 ^= 0xdd;

    TRACE;
    for (i = 0; i < dROUNDS; ++i)
        SIPROUND;

    b = v0 ^ v1 ^ v2 ^ v3;
    U64TO8_LE(out + 8, b);

    return 0;
}
